BIOCATALYTIC SYNTHESIS OF POLYMERS .3. FORMATION OF A HIGH-MOLECULAR-WEIGHT POLYESTER THROUGH LIMITATION OF HYDROLYSIS BY ENZYME-BOUND WATER AND THROUGH EQUILIBRIUM CONTROL

Enzyme-catalyzed preparation of polymers offers several potentially va luable advantages over the usual polymerization procedures and has bee n studied for several years. A significant limitation on the polyester s prepared to date has been the low molecular weights achieved. The pr esent studies have established that, in the polycondensation of bis(2, 2,2-trifluoroethyl) glutarate with 1,4-butanediol using porcine pancre atic lipase as the catalyst, this limitation arises from at least two sources: hydrolysis of activated ester and groups by water introduced along with the enzyme and the polymerization's reaching equilibrium de spite using the poorly nucleophilic 2,2,2-trifluoroethanol as the leav ing group. Evidence is also developed that the presence of trifluoroet hanol accelerates the release of the enzyme-bound water which hydrolyz es the activated ester end groups. The hydrolysis could be avoided by choosing a relatively high-boiling solvent, such as bis(2-ethoxyethyl) ether, then removing the trifluoroethanol by placing the reaction mix ture under vacuum periodically or by drying the enzyme rigorously. The vacuum method also removed the limitation on molecular weight resulti ng from the reaction's reaching equilibrium. A further improvement in the molecular weight to nearly 40,000 daltons, well within the range t hat is technically interesting, was achieved by using 1,2-dimethoxyben zene or 1,3-dimethoxybenzene as the polymerization solvent. (C) 1995 J ohn Wiley & Sons, Inc.